Functional domains of nucleolar phosphoprotein p120.

Nucleolar phosphoprotein p120 is a low abundance, proliferation-associated protein. Several functional domains have been characterized and are discussed here such as the antigenic domain recognized by a monoclonal antibody, the nuclear/nucleolar localization domain, phosphorylation domains of casein kinase II (CKII) and protein kinase C, a putative methylation domain and an RNA binding region. By sucrose gradient sedimentation analyses, protein p120 was shown to rapidly sediment with 60-80 S pre-rRNP particles but sedimented more slowly when treated with RNAse or salt suggesting binding to RNA. Nucleolar protein p120 differed from other nucleolar proteins such as C23 (nucleolin) and B23 (nucleophosmin) which sedimented more slowly near the top of the gradient.